fix: Resolve query fetch result in memory to avoid N+1 query problems (#266)

* fix: Resolve query fetch result in memory to avoid N+1 query problems

* fix: optimize to one dala loader query

Author: igdianov

graphql-jpa-query-schema/src/main/java/com/introproventures/graphql/jpa/query/schema/impl/GraphQLJpaQueryFactory.java

@@ -227,8 +227,8 @@ protected <T> Stream<T> getResultStream(TypedQuery<T> query,
         }
 
         // Let's execute query and get wrap result into stream
-        return query.getResultStream()
-                    .peek(entityManager::detach);
+        return query.getResultList()
+                    .stream();
     }
 
     protected Object querySingleResult(final DataFetchingEnvironment environment) {

graphql-jpa-query-schema/src/main/java/com/introproventures/graphql/jpa/query/schema/impl/GraphQLJpaToOneDataFetcher.java

@@ -16,9 +16,10 @@
 
 package com.introproventures.graphql.jpa.query.schema.impl;
 
+import static javax.persistence.metamodel.Attribute.PersistentAttributeType.EMBEDDED;
+
 import java.util.Optional;
 
-import javax.persistence.metamodel.Attribute.PersistentAttributeType;
 import javax.persistence.metamodel.SingularAttribute;
 
 import org.dataloader.DataLoader;
@@ -27,6 +28,7 @@
 import org.dataloader.MappedBatchLoaderWithContext;
 
 import graphql.GraphQLContext;
+import graphql.language.Argument;
 import graphql.language.Field;
 import graphql.schema.DataFetcher;
 import graphql.schema.DataFetchingEnvironment;
@@ -55,11 +57,12 @@ public Object get(DataFetchingEnvironment environment) {
         GraphQLType parentType = environment.getParentType();
 
         Object source = environment.getSource();
+        Optional<Argument> whereArgument = queryFactory.getArgument(field, "where");
         Boolean isOptional = queryFactory.getOptionalArgumentValue(environment,
                                                                    field,
                                                                    attribute);
         // Resolve collection query if where argument is present
-        if (isOptional && !PersistentAttributeType.EMBEDDED.equals(attribute.getPersistentAttributeType())) {
+        if ((whereArgument.isPresent() && isOptional) && !EMBEDDED.equals(attribute.getPersistentAttributeType())) {
             Object parentIdValue = queryFactory.getParentIdAttributeValue(source);
             String dataLoaderKey = parentType.getName() + "." + Optional.ofNullable(field.getAlias())
                                                                         .orElseGet(attribute::getName);